In textile machines, especially DD twisters and other double-twist spinning machines, provided with a multiplicity of bobbins from which yarns can be fed to the respective yarn packages, it is desirable, for various purposes, to be able to individually and independently terminate rotation of each yarn package.
For example, it is necessary to bring the respective yarn package to a standstill when there is a break in the thread fed thereto since knotting of the yarn ends is then required. It is also desirable to halt rotation of the yarn package when the bobbin or spool from which the yarn is fed to the package must be removed (i.e. is empty) and replaced.
In addition, it is desirable to selectively bring the takeup spool or yarn package to standstill when a predetermined length of yarn has been wound thereon or when the takeup spool has the desired diameter for further processing.
It is important to bring the yarn package to standstill without an extensive free-running contact between the takeup spool or package and the coiling cylinder which frictionally drives the package by contact with the periphery thereof, since a constant friction is otherwise applied to the outer turns of the yarn and may cause them to become loose from the package and become tangled. In addition, continuous frictional contact of the aforedescribed type tends to damage the yarn on the surface of the yarn package or takeup spool.
To interrupt the drive between the takeup spool and the coiling cylinder which is used to rotate the spool or package, there have been two principal techniques.
In the first approach, the takeup spool or yarn package is rotatable in a spool frame which is swung upwardly to terminate the contact with the continuously rotating coiling cylinder upon which the yarn package otherwise rests. The swinging movement is effected by a lifting rod which is controlled by a thread monitoring device. Alternatively, a slider can be provided which is introduced between the yarn package and the coiling cylinder to separate the two.
In the second approach, the winding cylinder is decoupled (declutched) to disconnect it from the drive shaft so that both the takeup spool and yarn package and the coiling cylinder simultaneously are brought to standstill.
German published application (Auslegeschrift) DT-AS 1 785 410 discloses a device operating in accordance with the principles of the second technique, whereby the coiling cylinder is connected with the drive shaft with a jaw clutch.
The drive shaft is provided with a hub having an axially turned end face provided with a toothed crown, this hub being angularly fixed to the drive shaft, i.e. continuously rotated therewith without slip therebetween. The toothed crown engages a meshing toothed crown provided at an axial end of the coiling cylinder and hence drives the latter. The coiling cylinder is loosely journaled upon the drive shaft via antifriction or slide bearings. A permanent magnet in the rotating hub cooperates with a steel ring within the coiling cylinder to stabilize the meshing of the teeth of the confronting crowns thereof. Parallel to the coiling cylinder a rod is axially shiftable and carries at both ends actuating fingers which embrace the ends of the coiling cylinder as a shifting fork. Upon displacement of this rod parallel to the axis of the coiling cylinder, the teeth of the latter are withdrawn from engagement with the axially fixed hub.
A thread-sensor control device, responsive to thread breakage, laterally shifts the rod and its actuating fingers. One of the fingers is thus effective to draw the coiling cylinder out of engagement with the hub carried by the shaft along the latter. When the thread sensor is again brought into its operating position, the movement thereof causes a displacement of the rod in the opposite direction so that the other finger becomes effective to shift the coiling cylinder into meshing engagement with the toothed hub.
Since the takeup spool or yarn package rests with its entire weight constantly upon the coiling cylinder during the coupling and decoupling thereof from the drive hub of the shaft, the axial displacement of the coiling cylinder parallel to the longitudinal axis of the spool or yarn package and relative thereto readily rubs loose the outer turns of the yarn and/or damages them. Instantaneous connection and disconnection of the coiling cylinder after a thread break using the device described has been found, in practice, to cause downwardly hanging yarn ends to readily become engaged with the neighboring spindle and here induce a further thread breakage.
German utility model (Gebrauchsmusterschrift) DT-GbmS No. 7 126 199 also discloses a roller which has a braking surface. The latter, upon axial shifting of the roller against an oppositely turned braking surface by an electromagnet, causes coupling thereof. The electromagnet can be switched by circuitry triggered by a thread-guide device. So that the broken yarn end can be coiled up, the electromagnet is switched on through a time delay relay. This arrangement has been found to be relatively costly since, for each coiling cylinder, an electromagnet with associated electrical installation must be provided. In addition, the disadvantages arising upon axial shifting of the roller, as described above, remain.